As the demand on the device integration of an integrated circuit is gradually increased, the feature size of a semiconductor device (e.g. a field effect transistor) becomes smaller and smaller, and the thickness of a gate oxide layer of the field effect transistor is reduced. For maintaining the dielectric performance and reducing current leakage, the gate oxide layer of the semiconductor device is usually made of a high-k material. Moreover, since the doping capacity of the conventional polysilicon gate electrode is limited, the efficacy of using the doped polysilicon gate electrode to improve the threshold voltage is usually insufficient. Nowadays, for solving the problems resulting from reduction of the device feature size, the polysilicon gate electrode is gradually replaced by a metal gate electrode.
However, it is still a challenge for those skilled in the art to increase the working performance and the production yield of the field effect transistor.
Therefore, there is a need of providing an advanced method for fabricating a field effect transistor in order to improve the working performance of the field effect transistor and increase the production yield thereof.